Defining relative clauses

Defining relative clauses tell us which one of a group of things/people we are talking about. The sentence doesn't usually make complete sense without the relative clause.

• Defining relative clauses are not separated from the rest of the sentence by commas.
✓ This is the DVD which I told you about the other day.

• We can also use that to introduce the relative clause.
✓ This is the DVD that I told you about the other day.

• We can often leave out the word which introduces the relative clause when it is the object of the clause.
✓ This is the DVD I told you about the other day.

• Notice that we do not need a preposition when we use where or when.
✓ The theatre where I first acted is somewhere around here.
✘ The theatre where I first acted in is somewhere around here.
✓ Do you know the year when the first western was made?
✘ Do you know the year when the first western was made in?